Viruses and Prions
What is a bacteriophage?
Viruses that infect bacteria
What does nucleocapsid refer to?
Both the nucleic acid and the capsid
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What is a virion?
Fully formed virus able to establish infection in a host
What is a genome?
Total genetic information in an organism or virus
What is a host?
Organism in which smaller organisms (bacteria, fungi, protozoan parasites) and viruses live in, feed on and reproduce in
What is host range?
The types of host or host cells that a virus can invade
What is cytopathic effect?
Visible changes that can happen to cells from infection and can be seen using a microscope
What are inclusion bodies?
Masses of viruses and damaged organelles that can form inside cells
What are syncytia?
Virus-infected cells that fuse together
What is a provirus?
Viral DNA inserted into host DNA, dormant inside cell
What is a prophage?
Once viral DNA is inserted into bacterial chromosome
What is chronic latent state?
The dormant state, activation after a period of viral inactivity
What are the general properties of a virus?
Capsid- Protein coat that surrounds the nucleic acid
Envelope- Layer outside if capsid. Consists of lipids proteins and carbohydrates. Present in some animal viruses. Usually made from the host cells membrane
Spikes- projections form the virus. Help virus attach to host cell
Viruses carry DNA or RNA not both
Animal viruses are usually helical or icosahedral shape
Complex Capsids on found in phage, the virus that infect bacteria
Type of genetic material they carry affects how viruses replicate
1. Label parts (A-D) of an enveloped virus on the diagram. Know the purpose of each part.
A. Envelope- protects genetic material
B. Spike- Help virus attach to host cell
C. Capsid- protect the genome, deliver the genome, & interact with the host
D. Nucleic acid- encodes information virus needs to make copies of itself
Be able to identify the family and genus of a virus based on the ending of the name.
Viral species- group of viruses sharing the same genetic information and host range
Virus is used for genus names and Viridae is used for family names
Species name usually based on where they are found, animal host or disease it causes
Subspecies are stains
Know the sequence events in the life cycle of an animal virus. For each phase, know what key events occur.
Adsorption=attachment- invasion begins, virus adsorbs to specific receptors on cell membrane of host
Penetration=entry- 2 methods:
1. Endocytosis- entire virus is engulfed by the cell and enclosed in a vacuole or vesicle. Entire envelope makes its way into the cell.
2. Direct fusion- the viral envelope fuses with the cell membrane and releases the capsid into the cell (only in enveloped viruses). Only capsid makes its way
3. into the cell.
Uncoating- dissolving the outer covering, releasing the virus into the cytoplasm
Synthesis- making more viral parts and proteins (capsid, spike, enzymes (some viruses)). Mechanism varies depending on whether the virus is a DNA or RNA virus.
Assembly- "putting parts together." Viral spike proteins are insert it into the cell membrane for the viral envelope; nucleocapsid is formed from RNA and capsomeres
Release- enveloped viruses bud off of the membrane, carrying away an envelope with the spikes. This complete virus is ready to infect another cell. 2 methods:
1. Budding- only in enveloped viruses. Creates envelope of virus. "Pushes out capsid." Until it breaks off. It doesn't kill the host cell but doesn't mean the cell is still functional. Will be damaged wont do its normal job.
2. Rupturing- only in nonenveloped viruses. Literally bursts out of cell. "Will accumulate and explode." Will kill host cell
What types of viral proteins will the host cell make during the synthesis phase of the viral life cycle?
Capsid proteins, spike proteins, & enzymes (some viruses)
Where in an animal host cell do most RNA viruses replicate their RNA and make proteins?
In host cell cytoplasm
Explain the function of RNA-dependent RNA polymerase during synthesis of a (+) ss RNA.
Template to make more +RNA
Explain the difference(s) between sense and antisense strands of RNA.
Sense RNA can be read by ribosomes
Antisense RNA cant be read by ribosomes
Where in an animal host cell do most DNA viruses replicate their DNA?
In host cells nucleus
Where in an animal host cell are the viral proteins made?
In the cytoplasm
Where in an animal host cell are DNA viruses assembled?
In the nucleus
What is the function of the following retrovirus enzymes?
a. reverse transcriptase- enzyme that uses viral ssRNA as a template to produce complementary double-stranded DNA
b. integrase- enzyme helps insert dsDNA into the hosts chromosomes
c. protease- enzyme processes capsid protein
Describe how some viruses can increase the risk of a cell becoming cancerous?
Many oncogenic viruses integrate their DNA into the hosts DNA. The virus damages DNA in such a way that a normal cell becomes cancerous.
Describe the steps of the lytic cycle.
Adsorption- tail fibers lock into receptor
Penetration- inject viral DNA into cytoplasm
Duplication- makes viral parts
Assembly- put together viral parts
Maturation- fully developed
Release- virus directs host cell to make lytic enzymes that weaken bacterial cell wall. This causes lysis to kill bacterial cell. AKA why it's called lytic cycle
How does the lytic cycle differ from the lysogenic cycle?
Lytic cycle differs from lysogenic cycle by the penetration phase lytic cycle injects DNA into cytoplasm versus lysogenic cells inserts itself into the bacterial cell chromosome and remains dormant
How can lysogenic conversion lead to increased pathogenicity in bacteria?
If the genes code for things such as toxins